Gypsum composition



106. cov s-sums,

comma msuc Patented Aug. 11, 1942 GYPSUM COMPOSITION Manvel C. Dailey, Elmhurst, Ill., asslgnor to United States Gypsum Company, Chicago, Il l., a corporation of Illinois No Drawing. Application January 18, 1940, Serial No. 314,405

Claims This invention relates to an improved composition of matter especially adaptable for use in sealing of earth-bored holes, wells, earth dams, etc.

One of the objects of the present invention is a composition of matter consisting primarily of a form of calcined gypsum to which certain ingredients have been added so as to render the composition particularly suitable for use in the cementing of oil wells, the tamping of explosives in holes in the earth and preventing seepage under earth-fill dams, dikes, levees, and the like.

A further object is to provide such a composition in the form of a ready-mixed powder containing set-controlling ingredients which will overcome the set-disturbing conditions likely to be encountered in the use of the composition underground and under adverse conditions of time, pressure, agitation, and the like.

In the copending application, Serial No. 224,637, of Andrew c Hamilton, Jr., now issued as United States Patent No. 2,191,652, there are described methods of cementing oil wells and other types of earth-bored holes, earth-fill dams, etc., with calcined gypsum of predetermined time 5 of s et. A'calcined gypsum cement suitable for extensive use in this field must possess qualities not found in present known types of calcined gypsum products. Some of these more important requirements are:

1. UNIFoam'rY or Sm'rmo TIME UNDER Vxnxmo Counrrrons 0! MIXING AND AGITATION In actual use, these cements are subjected to varying amounts of mixing and agitation by the three agencies of slurry-mixing, internal agitation and mixing during the process of pumping through casings, etc., and the agitation caused by forcing the slurry against formations through which gas, water, or oil is escaping. Normally retarded calcined gypsum has its setting time markedly afiected by the amount or severity of the mixing which a slurry of the product receives. In general, the greater the amount of mixing or agitation to which present known types of calcined gypsum are subjected, the faster will be the setting time of the product. For use in earth-bored hole cementing operations it is important that the setting time of the product remain essentially the same under light or severe agitation, or under conditions of intermittent or continuous agitation.

2. Umronm'rr or Sm'rmo TIME IN Pansnucs or SET Accsmmrrvn 0a RETABDIVE MATEBIAIS A slurry of calcined gypsum cement being pumped into earth-bored holes, oil wells, etc., may come into contact with, and be contaminated by, many materials which markedly ac: felerateor retard the setting time of known prodof retarder, or other known colloidal retardive materials such as glue, casein, gelatin, etc., are; not stable as to their setting'time with age,

- saline waters containing varying proportions of alkali chlorid Epsom salts, alkaline bicarbouese sa a ac as set acce le rafirs nets of this type. Such materials may include lfldes, borates, or organic matter which act as e re arders. Further, n g muds used in ell amine operations may contain added chemcals such as sodium silicate which is a powerul accelerator, or sodium metaphosphate, which a powerful retarW 3. UNIFORMITY or Sm'nNo TIME IN Acme or THE DRY CEMENT UPON STORAGE Most commercial calcined gypsum cements designed to set in time periods of about 40 minutes or longer are retarded with what is commonly called "commercial retarder.

amine;

This retarder is A generally a keratinous protein material hydrolyzed with falkalis and'extended with a filler. 5

'c'aicifid gypsum rements containing this type Such cements may either quicken or lengthen; very appreciably in setting time upon storage, de-

gypsum employed, the eiiect of other materials in the cement, etc.

4. UNIFosm'rY or SETTING TIME UNDER TEMPERA- ru'sn VARIATIONS Particularly in deep il wells, high temperatures ranging frequently above 0 F. are encountered. Calcined gypsum cements retarded with commercial retarder are very susceptible to setting time changes at difierent temperatures. For example, a calcined gypsum retarded with commercial keratinous retarder has been found to possess setting times as follows, under varying conditions of temperature:

Temperature, F. Time of set .Minuies 450 (Net set in 12 hrs.)

Obviously, for use in deep wells at temperatures much in excess of F. such a cement would not perform satisfactorily.

5. Umoaurrr or RATE or HYDBATION on SET between the beginning of the stifiening of the mass and the se as determined by standard pendent upon atmospheric conditions under,

A. S. T. M. methods. Present various types of prepared gypsum cements or set-stabilized calcined gypsum cements, for instance as msclosed the time of the initial stiffening of the slurry and the set of the material.

6. HIGH STRENGTH, Low Poaosrrr, AND Pnansmzuca While ordinary calcined gypsum possesses sufficient strength, when set, to function properly for some types of well-sealing operations, many such operations require a much higher degree of strength, density, and permanence than can be obtained with ordinary calcined gypsum. Uses requiring these qualities include the permanent cementing of surface casings or long strings, sealing of porous formations against water or gas under high pressure, bottom plugs employed for acidizing, tamping nitroglycerol, etc.

It is apparent that the above qualities must be present in any calcined gypsum cementitious composition designed for successful use under the extremely variable conditions which are encountered in oil well cementing operations. Uniformity of setting time, adequate strength development, and rate of hardening must be maintained under the most adverse field conditions, involving variations in mixing technique, aging, presence of set-modifying ingredients, and temperature variations.

Despite the fact that no known calcined gypsum composition has met all of the above requirements, I have succeeded in developing a composition which produces the results desired. This composition is in successful commercial use by the oil industry, many hundreds of tons are being sold, and its use is rapidly increasing.

The following formula has been found satisfactory, though it is obvious that the same may be varied without departing from the principles underlying this invention as defined in the here- Consistency, as used herein, is defined as that amount of water in cubic centimeters which, when added to 100 grams of the material and thoroughly blended therewith, will provide a plastic mass of such flowability that it will Just pour in a continuous stream from the lip of a cup.

The alpha gypsum above mentioned is a lowconsisten'cyf'highstrength, stable type of calcium sulfate hemihydrate, manufactured by the calcination of gypsum under pressure, as described and claimed in Randel and Dailey Patent a No. 1,901,051. Its use in the above composition enables me to obtain strengths 200-300 than the strengt u e" W1. the use of *e ordinary types of calcined gypsum calcined under normal atmospheric pressure.

Sodium, potassium, or any alkali metal bisulfaE, when employed in combin' ation with an excess of Portland cement, lime, basic slag, or other basic ma ena capa e mrmmg C8.(OH)2 by hydrolysis upon dispersion in water, enables me to obtain a very satisfactory degree of set-stabilization against such set-disturbing influences as variation in time and intensity of mixing or agitation, contamination with set-accelerating or retarding materials, etc. I have found that 5 heayz metal acid reacting sulfates, such as al num e 4 a; me e sulfate NiSO4; ferrous sflfate R554; co er suB'ate EuSOu etE., are unsatis' facfir? for use in my composition. when such sulfates are used, the amounts of my preferred types of retarders required to produce a given time of set are greatly increased. Furthermore, the setting times are erratic, and the consistency of the composition is increased, with a corresponding decrease in strength and in hardness, and a loss of permanence. I ascribe this action to the chemical combination of the metallic radical of the above-named sulfates with the water-soluble retarder employed, with the formation of an ins' oluEle metallic retarder salt which is inoperative as a retarder upon the mixing of my cement with water. Whether or not this is the true explanation of what occurs, the result is as described. By the use of an alkali metal bisulfate, which does not react with my preferred types of water-soluble set retarders to produce insoluble salts, the desired combination of set-stabilization, strength, low consistency and set-regulation is achieved.

The addition of arabic in combination with lime or Portlan bent, or similar limeliberating material, enables me to reduce the consistency of my cement, thereby obtaining an increase in strength and in permanence, and a decrease in porosity, which thus enhances the value of the composition for certain uses as hereinbelow described.

For purposes of illustration only, a composition prepared as above, except that the consistency-reducing ingredients were absent, when prepared at a normal consistency of 43 cc. had a wet compressive strength of 1650 pounds per square inch; whereas, upon the addition of consistency-reducing ingredients, the consistency was reduced to 30 cc., and the wet compressive 45 strength was increased to over 3000 pounds per square inch.

Portland cement, hydrated lime, basic slag, or material capable of forming C8.(OH)2 by hydrolsis u on r on in wa er serve the following unct1ons my preferred composition: They furnish Ca(OH): to react with the alkali metal bisulfates with the formation of set-stabilizing CaSO4.2HzO c stals upon additiom) the cement, in accordance with the following typical reaction:

NaHSO4+Ca (OH) z+HzO CaSO4.2H1O+NaOH Such alkaline-reacting products tremendously increase the effectiveness of certain types of water-soluble retarders. Tartaric acid and soluble tartrates, for example, are very powerful retarders in the presence of Ca(OH)2. In neutral or acid-reacting calcined gypsum cements their retarding effect is negligible. Further, these calcium-hydroxide-containing materials produce an alkaline-reacting cement which inhibits corrosion of the steel casings, pipes, etc., with which the set cement comes into contact.

I prefer to add sufficient alkaline material of the type above described to satisfy the chemical requirements of all of the acidic constituents present, plus an excess ranging up to 5%, based on the total weight of all of the constituents of the cement. In certain cases it is desirable to employ mixtures of Ca(OI-I)zforming materials, such as, for example, Portland g emegt and hydrated lime, to obtain the maximum consistma mnnnsn and maximum set-stability against the effects of aging, etc.

I have discovered that certain crystalline water-solublg retarders are very effective when I used in com ma ion with set-stabilizing chemicals of the types described herein in producing calcined gypsum cements of stable setting time under varying storage conditions and under varyging temperatures up to about 175 F. Retarders of this type include citric acid and wa't'r 'so'luble citrates, tartaric acid and water-solulile Ertra es in e presence of alkaline reacting cemflfigsoluble borates tannic acid, hosphates, etc. Of the above, the citrates, tar rates, and

phosphates are particularly effective. Combinations of two or more of these retarders have been found in some cases to produce better results than the use of one of the constituents employed alone. For example, the following cement possesses the qualities above indicated:

Formula II Parts "Alpha gypsum 1975 Portland cement l5 Powdered gum arabic 6 Potassium acid sulfate 2 Tartaric acid Sodium hexametaphosphate 1 For purposes of comparison, setting times under similar test conditions are shown for a cement formulated as above, except that the tartaric acid and phosphate were replaced by commercial retarder in an amount suilicient to produce a cement of about the same setting time as the above, tested when freshly made at a temperature of 75 F. It will be seen from the following nor were and after storage anywhere nearly alike.

Testing conditions Time of set (Vicat needle-standard A. S. T. M. method) (minutes) Watersoluble retarder-s Commercial colloidal retarder Fresh cement, tested at 75 F 135 120 Fresh cement, tested at 150 F 150 450 Cement tested at 75 F. after 1 week storage at 85 F., 65% re]. humidity 132 195 The amount of retarder employed will depend upon the desired setting time of the composition. For use under conditions where extremely high strength is not required, I may elect to use rdicalcined gypsum cements of the type required for the purposes of the present invention.

For certain specific uses such as, for example, where my cement is employed in sealing ofi water in rather tight or relatively impervious rock formations, it is desirable that a slurry of the cement penetrate as far as possible into the interstices of the formations. I have found that improved penetration of such tight formations is obtained with my cement by incorporating therewith small amounts of wetting agent s, whose presence acts to reduce the surface tension of a water suspension of the cement. Sulfonated oils, al 1 aryl onates, sodium salts of sifilonated 1g er a co 0 s suc as lauryl alcohol, etc, are examples 0 my pre erre ypeso we mg agents. Amounts used will vary from 0.1 to 10 pounds per ton, dependent upon the efllciency of the wetting agent and the degree of surface tension reduction required. I prefer to use wetting agents of such chemical composition that they will not be precipitated as insoluble calcium salts when added to water in the presence of calcium sulfate and. calcium hydroxide.

e earths.

Alk lated aromatic mononuclear drocarbon sul fonates are especially 'u n epresenceo a a The above examples are purely illustrative of some of the objectives attained by the use of this new and improved composition. It was further found that extensive mixing as well as agitation did not substantially affect the setting time of the composition or otherwise impair its usefulness.

Though the above formulae are purely exemplary, it is obvious that others can be developed,

without substantial variation from the principles of this invention as defined by the appended claims.

In employing the composition hereinabove described, it is mixed with a sufiicient amount of water to yield a flowable mass of a consistency appropriate to the manner of introduction employed, such as by pouring, pumping, etc. The composition may be varied as to its time of set, according to the conditions encountered, and is primarily intended to be employed in accordance with the teachings of the inventions disclosed in the applications of Andrew C. Hamilton, Jr., copending herewith, Serial Nos. 224,637 and 304,467, new issued as Patents Nos. 2,191,652 and 2,210,545.

I claim:

1. A composition of matter particularly adapted for sealing earth formations comprising calcium sulfate hemihydrate in major amount, minor amounts of set-modifying ingredients comprising a water-soluble crystalline retarder and an alkali metal acid sulfate, gum arabic, and a sufficient amount of an alkaline-reacting calcium compound to render the composition slightly alkaline when mixed with water.

2. A composition of matter particularly adapted for sealing earth formations, characterized by its stability as to setting time over long periods of time and its resistance to adventitious set-disturbing influences, comprising:

Pounds Calcium sulfate hemihydrate 2000 Alkali metal acid sulfate 1/2-10 Portland cement 1-50 Gum arabic 2-20 Water-soluble crystalline retarder 0-10 5. A composition particularly adapted for sealing earth formations comprising Parts Alpha gypsum 1975 Portland cement l5 Powdered gum arabic 6 Potassium acid sulfate 2 Tartaric acid 1/2 Sodium hexametaphosphate 1 MANVEL C. DAILEY.

czmrzcmn OF comcnou. I Patent-Io. 2,292,616. Augugt 11, 19LL2.

mm c. mum.

It is hereby certified. that error appear; in the printed specification or the mid numbered Patel-t requiring con ection as follows: Page 1, secondeolw'nn, line k9, 1nthe table, aecond column thereof, for (Net set in 12 bra)" an "(int m: in 12 mm); and um; the and Letters Pm Should be reiad witfi thi correction therein'the t'the same may ponform to the rocprd' or the ca ae in the Patent Office.

Signed and sealed an. 291:: day of September, A. 9. 191m.

. .Henry Van Arsdale, (8031) Acting Corinhiasionerof Patents. 

